Transplantable mouse pituitary TSH secreting tumors will be utilized as models of thyrotroph function to study the regulation of TSH secretion and production by secretagogues and to determine if thyrotropin releasing factor acts by stimulating adenylate cyclase and/or affecting transmembrane calcium flux. These cells will be utilized to determine if triiodothyronine (T3) inhibition of TSH production is associated with T3 occupancy of specific nuclear receptors. The role of cyclic AMP in mediating insulin secretion will be studied by correlating the effects of various secretagogues such as glucose, glucagon and beta agenists on cyclic AMP levels and insulin release in a homogeneous population of beta cells obtained from a transplantable hamster insulinoma. To explore the mechanisms of cyclic AMP action, antibodies to cyclic AMP-dependent protein kinases will be utilized to study the heterogenity, production, degradation and state of association of these kinases.